1. Field of the Invention
The invention relates, generally, to the control of an internal combustion engine and, more specifically, to the initial control of an engine that mandatorily requires the engine to warm-up and reach a predetermined operating temperature before allowing the engine to be accelerated.
2. Description of the Related Art
Systems and methods for the control of internal combustion engines are well known in the art and are employed in numerous ways to regulate and control various aspects of the operation of the engine and the vehicle or device with which it is employed. The conventional practice of engine control utilizes electronic control units that consist of some type of processing device that operates upon a stored program to oversee the engine operating parameters. The electronic control units communicate with a variety of sensing devices and operate numerous actuators and active devices. The control is directly responsive to operator inputs relating to selective throttle commands, with the electronic control unit attempting to provide the optimum engine output while considering the wide variety of environmental, ambient, and dynamic conditions received through the sensing devices. In automotive applications, this control of the engine is based on operator throttle requests that result in movement of the vehicle. The electronic control unit will cause the engine to produce the requested torque while using the stored programming to optimize the efficiency of the torque output to provide forward momentum. For a given load condition, such as moving the vehicle from a standing start, increasing the engine torque generally causes an increase in the speed of the engine.
During warm-up periods of engine operation, when an engine is started from an initial temperature that is well below the predetermined normal operating temperature, it is desirable to provide specific engine control relating to engine temperature. In automobile and vehicular applications this most often takes the form of setting an increased idle speed, or xe2x80x9ccoldxe2x80x9d idle operating scheme while the engine warms up. This control scheme still allows the operator to increase the engine speed and operate the vehicle, while preventing engine stalling when the engine returns to an idle state prior to reaching its full operating temperature. The cold idle control scheme may provide control over the fuel/air ratios, valve and ignition timing, or any other engine subsystem controlled by the electronic control unit and may be directed at emissions output and engine efficiency as well as stall prevention. The cold idle approach to engine control is generally adequate for motor vehicle operation. However, it presents several drawbacks if used in the control of an internal combustion engine used, for example, in an industrial application.
When an internal combustion engine is employed in an industrial application, the engine output is generally considered in terms of either engine speed or engine torque. The control of engine torque output is used in respect to the specific loading to be placed on the engine without regard for changes to engine speed. The idea being to control the specific amount of engine torque delivered to the associated transmission so that the transmission is loaded within its operating limits. As the load, or work, on the engine increases, the engine speed is allowed to decrease to maintain the application of a desired engine torque. As the load decreases, the engine speed is allowed to increase.
The control of engine speed is used in situations where the speed of the engine must remain a constant despite a changing load condition. One example of this type of application includes an alternating current electrical generator where the output frequency of the alternating current is dependent upon the engine speed. In this representative example, as the load on the generator increases, the torque produced by the engine must increase in order to maintain the constant engine speed, and thus a constant generator output frequency. The desired speed of the engine may be operator controllable through a speed request input to an electronic control unit, so that the control unit drives the engine as necessary to maintain its speed.
Many industrial engine applications require the engine to operate in one or more of these modes at different times, and sometimes simultaneously. For example, a self-propelled highway-compatible crane operates in the torque control mode when traveling on the highways. Once at a job site, the crane""s engine is switched to operate in the speed control mode for proper operation of the crane assembly. When started from a cold state condition, it is undesirable to operate these industrial engines without a warm-up period to bring the engine to operating temperature. A warm-up period is required to prevent damage to the engine and to prevent stalling of the cold engine under load.
Internal engine damage can occur when the engine fluids, most importantly the lubricant oil, are cold and viscous on first starting the engine. As used herein, the term xe2x80x9ccoldxe2x80x9d refers to the condition where the engine and its operating fluids are below a predetermined temperature such that the fluids are too viscous to function adequately for their intended purposes. For example, during periods of non-activity, the engine oil drains or bleeds off many of the internal bearing and interacting surfaces of the engine. Then, when the cold engine is started, these surfaces may lack, or have very little of, the necessary engine oil film to protect them from the metal-to-metal contact in the first minutes of operation. Additionally, with the components of the engine cold, the tolerances between the moving parts are at their greatest. Thus, if a working load is applied to a cold engine, the lack of lubrication and greater tolerances can cause greater wear among the engine components. A cold engine placed under load may also develop hot spots within the cooling jacket until the coolant warms and begins to flow. This condition may ultimately result in localized heat related weaknesses in the engine components. Additional operational considerations are an excessive white smoke output from a cold engine and a reduction in fuel efficiency.
Cold engine stalling can occur due to the fact that a cold engine is difficult to control with even the most sophisticated engine controls. For example, the incoming fuel may coagulate and prevent proper atomization, and the engine coolant may be relatively static. In these operating conditions, the combustion reaction is difficult to control and maintain. Nevertheless, operators sometimes request engine torque or speed prior to the conclusion of a proper engine warm-up period.
Merely applying the cold idle scheme of an automobile or other motor vehicle, as described above, fails to provide for a proper warm-up period as it merely increases the idle speed while still allowing an operator input to increase engine torque or speed output without regard for engine temperature. Additionally, known methods of governing industrial engines for torque and/or speed limiting do not address the need for a warm-up period. Therefore, it is most often left to the operator to subjectively allow for a proper engine warm-up period. As noted above, the drawback inherent with this approach is that an operator can indiscriminately request a torque or speed increase without waiting for the engine to reach the proper operating temperature, and in this case, the engine may respond with detrimental results. For example, the engine can stall such that a load may be dropped and/or the engine could sustain mechanical damage. Thus, there is an ongoing need in the art to provide for a mandatory engine warm-up period for internal combustion engines that are controlled as a function of their torque and/or speed outputs.
The present invention overcomes the disadvantages of the related art by providing an engine control system that imposes a mandatory warm-up period. The engine control system includes an electronic control module (ECM) having a torque inhibit circuit and a speed inhibit circuit, and an at least one engine fluid temperature sensor in electrical communication with the torque inhibit circuit and the speed inhibit circuit of the ECM. The sensor is exposed to at least one engine fluid. The sensor is adapted to provide an inhibit signal to the torque inhibit circuit and to the speed inhibit circuit of the ECM indicative of the temperature of at least one fluid within the engine. The torque inhibit circuit and the speed inhibit circuit are operable to cause the ECM to disregard any requests from an operator commanding an increase in engine torque or engine speed until such time as the inhibit signal from the temperature sensor exceeds a predetermined threshold.
The present invention also overcomes the disadvantages of the related art by providing a method of controlling an internal combustion engine so that it has a mandatory warm-up period. The method includes the steps of monitoring the temperature of at least one engine fluid and providing a signal indicative of that temperature to an ECM. The method will then inhibit any torque request signal from an operator until the engine fluid reaches a predetermined threshold and inhibit any speed request signal from an operator until the engine fluid reaches a predetermined threshold. The method then enables either torque requests or speed requests from an operator once the signal indicates that the engine fluid exceeds the predetermined threshold.
In this manner, the present invention provides a mandatory, controlled, and uninterrupted warm-up period for an internal combustion engine from a cold start condition to its predetermined operating temperature so that engine damage and excessive wear is prevented. These two undesirable effects are avoided by allowing the engine fluids, such as the lubricating oil, to reach a temperature range where they are most effective before loading the engine. Additionally, the components of the engine are allowed to reach a heated and stable condition so that the tolerances of the engine reach the proper state before allowing the operator to command increases in engine torque or speed outputs to load the engine. This also precludes the common white smoke output of a cold engine and maintains good fuel efficiency.
Another advantage of the present invention is that it removes the safety hazards concerned with operating a cold or improperly warmed engine under load. A cold engine generally operates inefficiently to the point of balking and stalling. If an operator is allowed to command increases of torque or speed output from a cold engine, a balk or stall could cause a load weight to be dropped or a tension on a cable to be lost, for example. Such a failure obviously poses a great physical threat to the operator or those working in the immediate vicinity. Accordingly, engine control system and method of controlling an internal combustion engine having a mandatory engine warm-up period of the present invention eliminates these concerns.